1. Field of the Invention
The present invention relates to DC (direct current) brushless motors, light deflectors, optical scanning devices, and image forming apparatuses such as electrophotographic copiers, printers, facsimile machines, and multifunction machines having two or more of these functions.
2. Description of the Related Art
With respect to electrophotographic recorders such as digital copiers and laser printers using a laser writer having a light deflector, light deflectors that rotate at high speeds greater than or equal to 20,000 rpm (revolutions per minute) have been put to practical use with increases in printing speed and pixel density. DC brushless motors such as those described below are used to rotate these light deflectors.
Japanese Laid-Open Patent Application No. 2000-050603 discloses a four-pole, twelve-coil DC brushless motor as an example of the n-pole, 3n-coil type (n=even number).
Japanese Laid-Open Patent Application No. 2001-251831 discloses a DC brushless motor in which magnetic bodies are disposed on the open magnetic path side of rotor magnets. According to this DC brushless motor, magnetic fluxes emanating from the rotor magnets are attracted to the magnetic bodies, so that magnetic fluxes entering other fixed members disposed around the rotor magnets are reduced. As a result, eddy current generation is reduced in the other fixed members. Meanwhile, eddy currents are generated inside the magnetic bodies, but are reduced in magnitude because there is a great distance between the rotor magnets and the magnetic bodies disposed on the open magnetic path side of the rotor magnets. Accordingly, eddy current generation is reduced in the entire DC brushless motor, so that a rise in the temperature of the DC brushless motor due to eddy current loss is reduced.
Japanese Laid-Open Patent Application No. 2003-177346 discloses a polygon scanner that is capable of high-speed rotation with low vibration at high temperatures, thereby achieving power saving and assembly simplification at the same time.
However, in the above-described conventional DC brushless motors, the number of magnetic poles and the number of coils are not optimized for light deflectors, so that a large amount of power is consumed and a large amount of heat is generated.